1. Field of the Invention
The present invention relates generally to a protective apparatus for a pick-up tube of a television camera and is directed more particularly to a protective circuit for a pick-up tube of a television camera used in a remote station of an interphone system including a master station.
2. Description of the Prior Art
In general, an interphone system includes a master station and one or more remote stations connected to the master station, and an inter-communication only by a vocal sound or conversation is possible between the master and remote stations. When the remote station of the interphone system is installed near the entrance or the like of a house, the interphone system is generally called as a door-phone system. In such a case, the interphone or door-phone system is used to know the coming of a visitor to a person in the house and also to ascertain who is the visitor.
By the way, almost all interphone system which are widely used at present are only for conversation between the remore and master stations thereof, and a visitor is ascertained through the conversation only. If it is possible to ascertain the visitor by his face and figure in addition to his voice, it is further desirable.
To this end, it may be considered that sound and video signals are both transmitted at the same time from the remote station to the master station when the visitor operates the remote station. In this case, a television receiver is installed in the master station while a pick-up tube of a television camera is installed in the remote station to transmit a so-called video signal from the remote station to the master station. Thus, the image of the visitor who operates the remote station can be reproduced on the television receiver installed in the master station.
In general, the remote station including the pick-up tube of the television camera of the interphone system is located outside the house, for example, on the gate or the like. In this case, when light such as the sun light having the intensity greater than a predetermined value is directly incident on the pick-up tube, there occurs such a fear that the target screen of the pick-up tube is damaged.